Our vessels

Now let's review the structure and operation of the vascular system, which carries driven by heart the blood throughout the body. We already know that the vascular system consists of arteries, capillaries and veins.
The largest vessel is aorta. We used to imagine the blood vessels in the form of more or less gentle tubes. So are completely unfamiliar with the size of the "tubes", almost equal to the thickness of hands at the wrists. From the aorta depart arteries to all organs of the body. The first turning away from the right and left coronary or coronary artery, which go deep into the muscle of the heart and provide it with all necessary. It is clear that these arteries and their branches are among the most important vessels of the body.
Entering the body artery branched into smaller vessels. The smallest of them, after which already begin capillaries are called arterioles. Their characteristic feature is the presence of a particularly well-developed layer of muscle fibers in the wall of the vessel, which therefore can significantly change their clearance. It must be emphasized that the arteries are generally characterized by the presence of a layer of muscles in the wall.
After arterioles begins dense network of capillaries. These finest vessels, there are a few billion. Their total length is 100 thousand kilometers, i.e. 2.5 times the length of the equator. The wall of the capillary consists of only one layer of flat cells that makes it highly permeable dissolved in the blood of substances and gases. However, among these cells are separate cells muscular type that can "close" the capillary. In muscle, which currently does not work, open only 1/10-1/50 of its capillaries. When the muscle starts to work and needs to be strengthened blood circulation, its capillary network is fully open.
Carry blood back to the heart of Vienna are characterized by the fact that they have valves that do not allow the blood to return to the capillaries. Veins have more weak and thin walls than arteries. In the wall there muscle layer. Features of the structure of the veins arise from the fact that they are much lower than in the arteries, blood pressure. It is higher pressure her in the arteries and properties of the arteries as the stretched inside the elastic tube with muscle layer in the wall, and there was that after death, the blood moves from the arteries to the veins.